The House of Pleasure (5th) and The House of Merging (8th)

It can sometimes seem contradictory which planets rule over what in the zodiac when there are nuances. For example, if Mars represents our sexual nature and overall drive, but it rules the 8th house why is the 5th house associated with sex? The 5th house is associated with instant shine or light which is why it is more associated with flirting and casual dating. When we meet someone, we are not in love yet (unless you believe in love at first sight) but it is lust or instantly seeing what we like. The 5th house as a house the Sun shines on are things we can easily observe.

The 8th house traditionally has little to do with sex but very intense topics of "gaining" from inheritance, or dealing with debt/taxes, death - nothing all that fun. In the modern context, the 8th house is often associated with concepts of intimacy and transfromation. Though the 8th can represent "joint assets" since it is opposing the 2nd house of money and self-suffiency and self work, it also can indicate areas where we need others to gain more power or momentum. The 8th house is not just "our stuff"; it is the "stuff" of others.

When dealing with dating or casual flings, the 5th house is where to look. You can see someone's attitude or approach to dating through planets or even what sign is on the cusp. For example, a person with Libra on the cusp but Venus is in the 9th house may be easily interested in being around people who are different from them. They can easily fall for others due to an enhanced need for partnership (Libra) but also want to experience a lot (9th house).

The 5th house will not necessarily indicate marriage unless Venus, Juno, or another placement is present that is related to partnership. This is why what you are attracted to may not always match what you choose in a long-term marriage.